Screening device

ABSTRACT

To overcome the tendency for undersize particles, in a wet, loose, solid material being screened on a stationary screening device comprising inclined longitudinal bars, to follow the surfaces of the bars into an oversize fraction collection area: the lower end regions of the bars are directed downwardly and terminated at such points that undersize particles dropping from the lower ends will drop into an undersize fraction collection area.

United States Patent [72] lnventor Johannes Jongbloed Hoensbroek, Netherlands [21] Appl. No. 884,372 [22] Filed Dec. 11,1969 [45] Patented Mar. 30, 1971 [73] Assignee Stamicarbon N. V.

Maesenstraat, Heerlen, Netherlands [32] Priority Mar. 25, 1967 [33] Netherlands [31] 6704381 Continuation of application Ser. No. 714,985, Mar. 21, 1968, now abandoned.

[54] SCREENING DEVICE 5 Claims, 2 Drawing Figs.

[52] U.S. Cl 209/240, 209/268, 209/393 [51] Int. Cl B07b 1/04 [50] Field of Search 209/233, 314, 393-395, 98, 99, 268, 269, 274, 240, 259, 255; 210/433, 499

[56] References Cited UNITED STATES PATENTS 377,921 2/1888 Whittle 209/395X Primary Examiner-Frank W. Lutter Assistant Examiner-Robert l-lalper Attorney-Cushman, Darby and Cushman ABSTRACT: To overcome the tendency for undersize particles, in a wet, loose, solid material being screened on a stationary screening device comprising inclined longitudinal bars, to follow the surfaces of the bars into an oversize fraction collection area: the lower end regions of the bars are directed v downwardly and terminated at such points that undersize particles dropping from the lower ends will drop into an undersize fraction collection area.

Patented March 30, 1971 3,512,505

2 Sheets-Sheet 1 Patented Mar ch 30, 1971 Y 3,572,505

2 Sheets-Sheet 2 PIC-3.2

ivuz/vrae isw/wvfs a dA/qezom SCREENING DlEViCE This is a continuation of application Ser. No. 714,985, filed 2i, i968 and now abandoned.

BACKGROUND OF THE INVENTION Some screening devices are provided with inclined screening decks comprising screening bars, the upper ends of which are clamped and the lower ends of which are free and which are so arranged that they diverge horizontally towards the free ends over their entire lengths. The material to be screened is supplied at the top side of the upper ends, and the devices are provided with receivers for the sized fractions.

Screening devices of this type are known as grizzly screens and are much used for dry screening all kinds of material. They comprise inclined straight bars that are fixed only one one end and which slightly diverge towards the lower, free ends. The material to be screened slides from the clamped ends of the bars towards the free ends of the bars and screened while sliding. Since the slots between the bars become wider towards the discharge end and the bars remain movable because theyare clamped at one and only, the risk of particles getting stuck between the bars is small.

The invention aims at rendering screening devices particularly those of the grizzly type, suitable for sizing particles co'ntained in water. when a conventional grizzly screen was tested in a wet screening operation, it appeared that part of the water flowed along the barsand entrained grains of the smallest fraction, which thus found their way into the oversize fraction.

SUMMARY OF THE INVENTION According to the invention; the screening bars are bent down at their free ends and the vertical projection of these ends does not extend past the upper edge of the partition wall between the receivers for the sized fractions.

In a preferred form, the invention comprises, in a particulate material screening device including: a plurality of transversely spaced, similarly inclined, generally longitudinally directed bars which proceed generally downwardly, for wardiy; a first collection area beneath the bars for collecting undersize particles falling between the bars; a second collection area adjacent the foremost longitudinal extent of the bars for collecting particles which are so large as to fail to fall between the bars; the first and second collection areas being separated by a transverse wall extending below the bars;

an improvement for overcoming the tendency of some on dersize particles of particulate material being screened on the device, to follow surfaces of the bars into the second collection area, said improvement comprising: portions of said bars adjacent the lower ends of said bars being bent downwardly and terminated at such points that undersize particles dropping from the lower ends of said bars drop into the first collection area.

A good effect is obtained if the free ends of the inclined screening bars are bent downwards and backwards through such an angle that the ends are inclined in the opposite direction.

in general, the screening deck is mounted in a housing between the two sidewalls of which a crossmember supporting the screening bars extends. If the sidewalls do not diverge, a guide strip is preferably mounted to each sidewall and over the screening deck in the housing, which strip extends approximately parallel to the outermost screening bar from the end of I the crossmember to near the free end of the said bar. In this way a wall is obtained which closely adjoins the outermost bars.

BRlEF DESCRIPTION OF THE DRAWINGS The invention will be further elucidated with reference to a preferred embodiment shown in the drawing.

FIG. I. is a longitudinal vertical sectional view of a screening device according to the invention;

Fit]. 2 shows a fragmentary top plan view of part of the device of EEG; ll. i

DESCRIPTION OF THE PREFERRED EMBODIMENT In the embodiment shown in the drawings the screening device has a sheet-metal housing 1 with two sidewalls 2 and 3 and two end walls lb and 14. A stationary screening deck 4 is mounted at an inclination in the housing I. The screening deck 4 consists of screening bars 5 that are clamped at their upper-end portions and lie in a common plane. The angle of inclination of the screening deck may vary between 15 and 35, dependent on the friction coefficient between the material to be screened and the material of the screening bars; in a typical embodiment used for wet screening plastics particles, an angle of inclination of 25 was found to be very satisfactory.

The upper ends of the screening bars 5 are fitted in a crossmember 6 which extends between and is secured to the sidewalls 2 and 3 of the housing I. Aside from their being held or clamped by the crossmember 6, the bars 5 are unsupported over their entire length and can deflect vertically and horizontally fully independently of each other. The screening bars have a smooth outer surface and, in this embodiment, the same diameter, an also a uniform cross section from one end to the other, although this is not essential. The bars may be solid or formed by seamless metal tubing.

Two partition walls 7 and 9 divide the housing into three compartments. Compartment A to the left of wall 7 serves as a supply area for the material to be screened. in the embodiment shown, the material to bescreened, together with water, is pumped into compartment A through feed opening 15. The material and water rise in compartment A and flow onto the screening deck 4 by way of a doubled over, flat part 8 of wall 7 that lies over the crossrnember 6. Compartment B under the screening deck 4 is defined between two walls 7 and 9 and serves as a receiver for the undersize fraction. Compartment C situated beyond the ends of the screening bars 5 is limited by the partition wall 9 and the end wall It) and serves as a receiver for the oversize fraction.

As appears from the top view of the particular screening deck shown in PEG. 2, the bars 5 diverge horizontally, so that the distance between them gradually increases in the downstream direction, without the thickness of the bars being reduced from one end to the other. Due to the gradually increasing width of the slots between the screening bars, there is little or no tendency for the screen to become blocked.

As is shown in FIG. 1, the free ends 16 of the screening bars 5 are curved downwardly, the vertical projection of these ends not extending past the upper edge ll of partition wall 9.

In a typical embodiment the angle of inclination of the screening deck was 25 and the bent part had the shape of a arc of a circle, so that the extreme end portions 16 had an opposite inclination of 20. The embodiment performed very satisfactorily. These values are given only by way of illustration. In general, it can be said that at an inclination of the screening deck of between 15 and 35 the lower end regions of the screening bars should preferably be bent back so far that the ends have an opposite inclination of l5-70. Naturally it is not necessary for the bent end regions to follow the arc of a circle. In instances where the liquid entraining undersize particles clings quite tenaciously to the bars, the downstream end regions of the bars may proceed at least slightly beyond the partition wall I, provided that the ends are bent back sufficiently to cause wet material flowing or dropping from the ends, to land in the undersize collection compartment.

To obtain a proper adjoining between the sidewalls 2 and 3 of the housing 1 and the two outermost bars 5' and 5", respectively of the screening deck 4, the two sidewalls of the housing are provided, immediately over the screening deck, with two flanking guide strips l2, 13, the middle part of each running approximately parallel to the respective outermost screening bars 5', 5". Each of the strips i2 and 13 extends from one end of the cross member 6 to near the free end of the respective outermost screening bar, 5' or 5", and the strips prevent material falling through between the outermost screening bars I 5 and the sidewalls ofthe housing.

The screening device according to the preferred embodiment of the invention operates as follows: Granular material, e.g., a plastics granulate is pumped, together with water, into compartment A through feed opening 15. The water and the material then flow over the flat edge 8 and travel along the screening deck under the influence of gravity. The biggest pieces, e.g., agglomerates or clusters, which cannot fall through the screen, slid along the bars and arrive in compartment C, from where they are discharged conventionally. Most of the water and the smaller granules fall through the screening deck slots into compartment B. Any water flowing along the bars and entraining fine granules drips off the lower ends 16 of the bars and thus is passed into the compartment B which receives the undersize fraction.

Thus in its preferred fonn, as shown, the present invention provides a nonblocking and self-cleaning screening device which is especially suitable for sizing plastic granules and other loose solid materials contained in water and which is highly efficacious, simple, easy to manufacture, and inexpensive.

The invention also has applicability where the inclined longitudinal screening bars are not divergent, although screen clogging could than be a more likely occurrence. The liquid, of course, need not be water, and the invention can be expected to have utility where some undersize particles, for whatever reason, tend to follow the surfaces of the bars, rather than all falling through the screen between the bars.

The terms bend and bent, as used herein in describing the lower end regions or portions of the bars 5, are meant to define a state of existence rather than a method of fonning.

It should now be apparent that the screening device as described hereinabove possesses each of the attributes set forth in the specification under the heading Summary of the Invention" hereinbefore. Because the screening device of the invention can be modified to some extent without departing from the principles of the invention as they have been outlined and explained in this specification, the present invention should be understood as encompassing all such modificatons as are within the spirit and scope of the following claims.

I claim:

1. A stationary device having an inclined screening deck comprising a plurality of screening bars, means clamping the upper ends of the screening bars, the lower ends of the screening bars being free and diverging horizontally towards said free lower ends over the entire lengths of the screening bars; the screening device being constructed and arranged to receive material to be screened being supplied at the top side thereof, and having with receivers for undersized and oversized fractions separated by a partition wall having an upper edge, said screening device being characterized in that the screening bars are bent down at their free ends and the vertical projection of the upper edge of the partition wall between the receivers for the undersized and oversized fractions; said stationary screening device being further characterized in that the free lower ends of the screening bars curve downwardly and rearwardly through such an angle that the free lower ends are inclined in the opposite direction to the remainder of the screening bars.

2. The screening device according to claim 1, characterized in that the screening bars upstream of said free lower ends are inclined 15 to 35 with the horizontal and said free lower ends are curved arcuately so that the free lower ends are inclined at an angle of 15 to with the horizontal, in a direction opposite to the inclination of the screening deck.

3. in a stationary screening device for separating wet, loose, solid material into fractions of pieces of different sizes, said device comprising:

an inclined screening deck which is formed by a plurality of longitudinally inclined bars, adapted to receive the material to be separated, supplied with liquid at the top side of the said screening deck;

means clamping the upper ends of the bars, the lower ends of the bars being free; a partition wall having an upper edge and extending downwardly from a position spaced from the bars near the lower end of the deck, for separating material which discharges through the deck material which discharges off its lower end; and

said screening device being characterized in that the fr'ee lower end portions of the bars curve downwardly and rearwardly so that their extreme lower end portions are opposite inclined to the screening deck, whereas the vertical projection of said free ends lies no further longitudinally downstream of the screening device than about the vertical projection of the upper edge of the partition wall, so to enable liquid dripping from the lower extremities of the bars to fall to the same side of the partition wall as material discharging between the bars.

4. The screening device according to claim 3, wherein the screening bars upstream of said free lower ends are inclined 15 to 35 with the horizontal and said free lower ends are curved arcuately so that the free lower ends are inclined at an angle of 15 to 70 with the horizontal, in a direction opposite to the inclination of the screening deck.

5. The screening device according to claim 3, in which the screening deck is mounted in a housing including two opposite longitudinal sidewalls and the batman clamped at their upper ends by a crossmember extending between said sidewalls of said housing, said screening apparatus being characterized in that the bars diverge towards the lower end of the screening deck and guide strips are mounted to each sidewall and immediately, over the screening deck in the housing, which follow the course of the respective outermost bars over at least the main part of their length to prevent flow of material off the sides of the screening deck.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3:57 :5 5 Dated 3 97 Inventor s) Johanna S Jongbloed It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, col. 3, line 41, after "stationary" read --screening--.

line 52, after "projection" read --of said free ends lies no further longitudinally downstre of the screening device than about the vertical projection- Claim 3, col. line 2 after "deck" read --from.

line 25, delete "and".

Signed and sealed this Hrth day of September 1971 (SEAL) Attestt EDWARD I I.FLETCHER,JR. ROBERT GO'I'TSCHALK Attesting Officer Acting Commissioner of Pat 

1. A stationary device having an inclined screening deck comprising a plurality of screening bars, means clamping the upper ends of the screening bars, the lower ends of the screening bars being free and diverging horizontally towards said free lower ends over the entire lengths of the screening bars; the screening device being constructed and arranged to receive material to be screened being supplied at the top side thereof, and having with receivers for undersized and oversized fractions separated by a partition wall having an upper edge, said screening device being characterized in that the screening bars are bent down at their free ends and the vertical projection of the upper edge of the partition wall between the receivers for the undersized and oversized fractions; said stationary screening device being further characterized in that the free lower ends of the screening bars curve downwardly and rearwardly through such an angle that the free lower ends are inclined in the opposite direction to the remainder of the screening bars.
 2. The screening device according to claim 1, characterized in that the screening bars upstream of said free lower ends are inclined 15 to 35* with the horizontal and said free lower ends are curved arcuately so that the free lower ends are inclined at an angle of 15 to 70* with the horizontal, in a direction opposite to the inclination of the screening deck.
 3. In a stationary screening device for separating wet, loose, solid material into fractions of pieces of different sizes, said device comprising: an inclined screening deck which is formed by a plurality of longitudinally inclined bars, adapted to receive the material to be separated, supplied with liquid at the top side of the said screening deck; means clamping the upper ends of the bars, the lower ends of the bars being free; a partition wall having an upper edge and extending downwardly from a position spaced from the bars near the lower end of the deck, for separating material which discharges through the deck material which discharges off its lower end; and said screening device being characterized in that the free lower end portions of the bars curve downwardly and rearwardly so that their extreme lower end portions are opposite inclined to the screening deck, whereas the vertical projection of said free ends lies no further longitudinally downstream of the screening device than about the vertical projection of the upper edge of the partition wall, so to enable liquid dripping from the lower extremities of the bars to fall to the same side of the partition wall as material discharging between the bars.
 4. The screening device according to claim 3, wherein the screening bars upstream of said free lower ends are inclined 15 to 35* with the horizontal and said free lower ends are curved arcuately so that the free lower ends are inclined at an angle of 15 to 70* with the horizontal, in a direction opposite to the inclination of the screening deck.
 5. The screening device according to claim 3, in which the screening deck is mounted in a housing including two opposite longitudinal sidewalls and the bars are clamped at their upper ends by a crossmember extending between said sidewalls of said housing, said screening apparatus being characterized in that the bars diverge towards the lower end of the screening deck and guide strips are mounted to each sidewall and immediately, over the screening deck in the housing, which follow the course of the respective outermost bars over at least the main part of their length to prevent flow of material off the sides of the screening deck. 